Understanding standard potentials of redox couples

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Matthew Gutierrez 2D
Posts: 19
Joined: Fri Sep 25, 2015 3:00 am

Understanding standard potentials of redox couples

Postby Matthew Gutierrez 2D » Thu Jan 28, 2016 10:47 pm

In page 582 of the textbook, it states that "the more negative the standard potential of a couple, the greater its reducing strength." I thought that a negative standard potential meant that the anode was less likely to be oxidized. I am a bit confused after reading this. Here is what I understand so far:

1.) In a galvanic cell, a positive cell potential means that the cathode is on the right and that the electrons travel there.
2.) If the cell potential is negative, then the anode is on the right and the electrons travel from right to left.

In other words, I am confused about what the standard potential of a redox couple tells us when it is positive and what it tells us when it is negative. I would appreciate it if someone could clarify this. Thank you!

Pauline Tran 2G
Posts: 20
Joined: Fri Sep 25, 2015 3:00 am

Re: Understanding standard potentials of redox couples

Postby Pauline Tran 2G » Fri Jan 29, 2016 3:16 pm

When the reduction potential for a metal electrode is positive, it tells us that that metal ion is more easily reduced than a hydrogen ion as the standard reduction potential for a metal electrode is referenced to a standard hydrogen electrode. When the metal electrode is negative, it means that the metal ion is more difficult to reduce than the hydrogen ion.

For example,
2e– + Zn2+(aq) Zn(s) -0.76V
The negative reduction potential indicates that the zinc ion is harder to reduce, and thus a worse oxidizing agent, than the hydrogen ion.

2e– + Cu2+(aq) Cu(s) +.337V
The positive reduction potential indicates that the copper ion is easier to reduce than the hydrogen ion.

Also, a positive cell potential means that the cell reaction will occur spontaneously to the right. A negative cell potential means that the cell reaction will not proceed spontaneously.


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